For [b]Pencil and Screen simulation[/b], the original source is phet.colorado.edu/
However, it did not real show image for screen located at different place.
It only show the range of light source. And I do not think the intensity are being calculated.
For the image shown at http://www.yenka.com/en/Yenka_Light_and_Sound/attachments/y-t2-1-1.gif
I am not sure is it a real simulation or is it just an animation?
It is not difficult to create a similar animation. But I am not sure is it a visual effect and/or is it base on solid physics.
I do not think it is just a convolution of an image --- may be I am wrong.
It has to be a 3D simulation. And all the light paths need to be calculated to form the image.
It is a complicated task and we might really learn something new from the simulation.
The easiest way is to perform the simple experiment.
[quote]However i do not have the resources. [/quote]
I think you can find the resources you need. It is not difficult to buy a lens. (magnify lens is available at many stores). You can use a candle as a light source. And you will understand more if you perform the experiment by yourself.
Simulation is good for experiments which are difficult perform or for some physics concept which need more visual effect or dynamic process which are not easily observed.
Simulation will not replace experiment. Simulation and experiment have it's own role.
For some cases, simulation is better than real experiment.
For some cases, real experiment is better than simulation.